East Indian sandalwood oil has been described as being "perhaps one of the most precious perfumery materials from antiquity down to modern times, and its popularity has shown no signs of waning" [E. Guenther, "The Essential Oils", Vol. V, Page 173, D. Van Nostrand Company, Incorporated, New York (1952)]. This oil is widely used in perfumery and would be even more widely used except for its limited supply and high cost.
For many years a need existed for synthetic substitutes which could be used as sandalwood substitutes or as extenders. In 1977 Naipawer and Easter (U.S. Pat. No. 4,052,341) disclosed the compound 3-methyl-5-(2,2,3-trimethylcyclopent-3-en-1-yl)pentan-2-ol which was characterized by a tenacious fine soft woody odor similar to sandalwood oil and the naturally occurring santalols. This compound not only has a fine sandalwood odor, it is also more stable than the potentially labile allylic alcohols of beta- and alpha-santalol. [Naipawer and Easter also disclosed and claimed the unsaturated analog 3-methyl-5-(2,2,3-trimethylcylopent-3-en-1-yl)pent-3-en-2-ol]. A major advantage of this invention is the fact that the compound can be readily and economically prepared from inexpensive materials, i.e., campholenic aldehyde and 2-butanone (methyl ethyl ketone). Campholenic aldehyde, which is readily available from alpha-pinene epoxide, is a relatively inexpensive starting material.
After the Naipawer and Easter patent appeared, there was a flurry of activity in this area and a number of patents appeared claiming sandalwood-type odorants starting from campholenic aldehyde. In most instances, these patents differed from one another in the compound that was condensed with campholenic aldehyde, the manner in which the condensation was conducted or the chemical steps that were performed on the condensation product.
The activity of the analysis of sandalwood oil and the search for synthetic substitutes has been thoroughly reviewed. (See E. -J. Brunke and W. Rojahn, Dragoco Report (Engl. Frag. Ed.), No. 5, 67, (1980); E. -J. Brunke, ibid., No. 8, 187, (1981), E. -J. Brunke and E. Klein in "Fragrance Chemistry-The Science of the Sense of Smell", E. T. Theimer, Ed., Academic Press, New York, N.Y., 1982, pp 397-431; K. H. Shankaranarayana and K. Parthasarathi, Perfumer and Flavorist, 9, 17, (1984); and other references mentioned in those reviews.)
Based on a reading of the above review articles and the patents issued, it would appear that the prior art has exhaustively covered all of the more valuable odorants that could be made starting from campholenic aldehyde. Applicant, however, discloses herein the most intense and most valuable campholenic aldehyde derivative that has been reported to date, a derivative that has escaped characterization and appreciation by all the investigators who have exhaustively studied and reviewed this field.